It is well-known that microorganisms of Escherichia coli K12 strains are some of the preferred microorganisms for carrying out genetic engineering experiments. E. coli K12 strains have been preferred mainly for two reasons: first, the genetic make-up of these organisms is well-known, and, second, recombinant DNA guidelines from several countries insist on the use of this strain to carry out recombinant experiments. As a result, recombinant DNA technology has been developed to produce, on an industrial level, commercially interesting substances using the host-vector system of E. coli K12.
However, E. coli K12 strains do not have the sucrose fermenting capacity that other industrially successful microorganisms, such as Bacillus, Corynebacterium, Actinomyces and yeasts, have. Therefore, E. coli K strains cannot grow efficiently using raw materials, such as molasses, which contain sucrose as the main carbon source.
As a result of the preferences for using E. coli K12, an E. coli plasmid vector has been sought which could be used to confer sucrose fermenting characteristics to such microorganisms. In such circumstances, this plasmid would additionally have the ability to carry industrially profitable genetic information.
Such a plasmid vector would afford an additional advantage in assuring the stability of a culture of microorganisms containing this vector. Such stability would arise as a result of expression of the sucrose fermenting phenotype; when a culture medium with sucrose as the carbon source is utilized, only the cells carrying the plasmid are able to grow and multiply, as they alone would have the ability to ferment sucrose. In other words, if the cells were to lose the plasmid containing the commercially useful genes, they would also lose their sucrose fermenting capacity and would not be able to grow in the provided culture medium. This plasmid-mediated stability avoids the expense of the addition of large amounts of antibiotics to the culture medium to assure plasmid stability.